People with AF are more likely to suffer a stroke than people without AF. That's because their erratic heartbeats allow blood to pool and form clots in the heart. The clots can travel to the brain and block blood flow, causing a stroke.

One in 10 people over age 80 has AF. That number is likely to increase substantially in the next few years due to the aging of the population, says Daniela Poli, MD, of the Azienda Ospedaliera Universitaria Careggi in Florence, Italy.

"Among people aged 80 to 90, about one-fourth of strokes are attributable to atrial fibrillation," she says.

Bleeding Risk From Warfarin

Studies have shown that warfarin can cut stroke risk by up to 70%, Poli said here at the annual meeting of the European Society of Cardiology. Warfarin is also sold under the brand names Coumadin and Jantoven.

A known side effect of warfarin is dangerous bleeding, and the risk of warfarin-related bleeding increases with age, Poli tells WebMD. As a result, many doctors are reluctant to prescribe it to older patients, she says.

A second study presented at the meeting shows that only 49% of 213 people with AF over 80 were prescribed warfarin.

"But our study demonstrates a low rate of bleeding complications in older patients, suggesting that age in itself should not be considered a reason to forgo warfarin treatment," Poli says.

Warfarin vs. Newer Anti-clotting Drugs

The findings come at a time when newer warfarin alternatives like Eliquis, Pradaxa, and Xarelto and have been approved by the FDA or are awaiting FDA approval, Poli notes.

While studies show they may have advantages over warfarin, there is no information on their use in very old people, she says.

Pico presented results of the so-called EPICA Study. It's the largest study on very old patients taking warfarin to prevent stroke or dangerous blood clots.

The study involved 4,093 patients aged 80 to 102 who were being treated with warfarin for the first time. About 60% had moderate kidney damage.

Over a three-year period, 179 suffered a serious bleed. That's equivalent to about 2% of patients per year.

The most dangerous type of bleeding -- into the brain -- occurred in 53 patients. That translates to 1% of patients annually.

People on warfarin are given frequent blood tests to make sure they are getting appropriate doses. If too much is given, you can suffer a dangerous bleed. Take too little and the risk of a potentially deadly blood clot increases further.

In the study, the older patients were in the correct dosage range about two-thirds of the time. That's similar to the figure reported in studies of younger patients.

American Heart Association President Gordon Tomaselli, MD, tells WebMD that he treats all his patients who are 80 and over with atrial fibrillation with warfarin or a newer anti-clotting drug "because they are the folks most likely to benefit in terms of reduction in stroke."

These studies were presented at a medical conference. The findings should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.